The objective of the proposed research are as follows: (1) Test the hypothesis that 5-hydroxytryptamine (5-HT) is involved as a nerurotransmitter in the non-adrenergic inhibitory innervation of the gut. (2) Determine the properties of 5-HT mechanisms in the myenteric plexus such as transport, storage and synthesis of the amine, and how these are affected by drugs. (3) Compare 5-HT mechanisms in the myenteric plexus with those of 5-HT containing, neural-crest-derived endocrine cells such as enterochromaffin cells of the gut and parafollicular cells of the thyroid. (4) Determine the fuction of 5-HT in the thyroid and its relationship to the polypeptide calcitonin, which appears to share storage vesicles with 5-HT. (5) Establish the role of pontine 5-HT neurons in the regulation of electrical activity, characteristic of REM, in oculomotor and visual systems (PGO waves). (6) Apply what is learned from studying the myenteric plexus to the PGO system to help establish the validity of using the myenteric plexus as a model for the less accessible 5-HT neurons of the central nervous system.